Conventional internal combustion engines operating on either a two-stroke or a four-stroke cycle commonly use a crankshaft and con rod arrangement to convert linear motion of a piston to rotary motion at an output shaft. Due to the crankshaft and con rod geometry, maximum piston acceleration generally occurs when the piston is at top dead centre (TDC), where piston acceleration is significantly greater than at bottom dead centre (BDC).
High piston acceleration at TDC poses several problems for engine performance. For example, in a spark ignition engine, the reduced TDC dwell time (time spent at or near TDC) associated with increased TDC piston acceleration increases the required spark advance, therefore reducing efficiency, particularly at high engine speeds. In a compression ignition engine the reduced TDC dwell time decreases the engine speed limit which is limited by the burn speed of the fuel. The difference in piston acceleration at TDC and BDC also requires a compromise to be made when designing the engine counterbalancing system, so the engine is less well vertically balanced. In addition, the high maximum acceleration forces experienced at TDC inflict severe stresses on engine components, therefore increasing the design requirements and the weight of the engine and reducing the lifespan of the con rod and piston. The problems associated with high accelerations and increased component loading at TDC are not confined to internal combustion engines but apply generally to any piston arrangement for converting reciprocating linear motion to rotary motion or vice-versa, for example a pump.
Several alternative engine arrangements are known which use different combustion chamber to output shaft coupling mechanisms to reduce maximum piston acceleration and increase TDC dwell time. For example, the Pattakon Greco engine, the Bourke engine, the Revetec engine and the Wankel engine all use different mechanical coupling solutions to address the above-mentioned problems. However, each of these alternative coupling arrangements suffers from several disadvantages. For example, the Pattakon Grekko, Bourke and Revetec engines all transmit a drive force from a piston to an output shaft via a line contact patch, resulting in high stress concentrations and increased wear rates. The Pattakon Grekko, Revetec and Wankel engines also require the machining of complex, high-precision cam shapes, which are difficult and expensive to manufacture.
In addition to the problems mentioned above, conventional two-stroke engines also suffer from problems with lubrication of the crankshaft and con rod assembly. The crankshaft and con rod assembly is generally housed within a crank case forming part of the induction system. The lubrication system operates as a total loss system in which lubricating oil is continuously fed into the crank case and allowed to pass into the combustion cylinder and thence out of the engine. This total loss lubricating system is both expensive to run due to the need to continuously replace the lubricating oil and damaging to the environment due to the presence of lubricating oil in the exhaust gases. The use of the crank case as a supercharging or induction chamber also limits the ability of engine designers to optimise the volume and shape of the induction chamber to maximise performance and efficiency of the engine.